Image reading apparatus

1. An image reading apparatus comprising: an image reader having at least one line sensor for optically reading an image carried on an image placed on a subject table and producing an image signal; and a sensor displacing unit for displacing said image reader in a main scanning direction of said line sensor; said sensor displacing unit comprising: a support base; a vibratory base disposed displaceably with respect to said support base, said image reader being fixed to said vibratory base; a piezoelectric device for displacing said vibratory base, said piezoelectric device having a vibration generating region; and an attachment unit by which said piezoelectric device is detachably fixed to said support base, with said vibration generating region being held against said vibratory base.

2. An image reading apparatus according to claim 1, wherein said vibratory base is defined by a slit which is defined in said support base and has opposite ends bent toward said image reader fixed to said vibratory base, and recesses defined in said support base along said opposite ends of the slit, leaving thin walls between said opposite ends and said recesses, so that said vibratory base is displaceable with respect to said support base.

3. An image reading apparatus according to claim 2, wherein said opposite ends of the slit and said recesses have curved corners which have the same radius of curvature.

4. An image reading apparatus according to claim 1, wherein said attachment unit comprises: an adjustment member for fixing said piezoelectric device and adjusting a projection length of said piezoelectric device; and an attachment member for installing said piezoelectric device on said support base with said adjustment member accommodated in the attachment member.

5. An image reading apparatus according to claim 4, wherein said attachment member has a surface on which said adjustment member is placed, said surface having a plurality of spaced threaded holes defined therein, said adjustment member having a horizontal holder for horizontally holding said piezoelectric device and a plurality of positioning oblong holes defined therein for passage therethrough of a plurality of adjustment bolts threaded into said threaded holes, respectively.

6. An image reading apparatus comprising: at least one line sensor having an array of photoelectric transducer elements as pixels, for reading signal charges stored respectively in said photoelectric transducer elements in response to an external reading clock signal and outputting the signal charges as image signals; sensor displacing means for displacing said line sensor to a plurality of positions in a main scanning direction along the array of the pixels in response to an external drive clock signal; storage means for storing the image signals from said line sensor in each of said positions; image signal arranging means for arranging said image signals in a sequence of the pixels in said main scanning direction and storing the arranged image signals in said storage means; and timing adjusting means for adjusting times at which said reading clock signal and said drive clock signal are outputted so that said reading clock signal is output after said drive clock signal.

7. An image reading apparatus according to claim 6, wherein said timing adjusting means comprises means for adjusting said times to introduce a time interval therebetween which corresponds to a pixel shift in said main scanning direction which is caused in an image reproduced from the image signals when said line sensor is displaced by said sensor displacing means.

8. An image reading apparatus comprising: at least one line sensor having an array of photoelectric transducer elements as pixels, for reading signal charges stored respectively in said photoelectric transducer elements in response to an external reading clock signal and outputting the signal charges as image signals; sensor displacing means for displacing said line sensor to a plurality of positions in a main scanning direction along the array of the pixels in response to an external drive clock signal; storage means for storing the image signals from said line sensor in each of said positions; image signal arranging means for arranging said image signals in a sequence of the pixels in said main scanning direction and storing the arranged image signals in said storage means; and timing adjusting means for adjusting times at which said reading clock signal and said drive clock signal are outputted, wherein said timing adjusting means comprises means for adjusting said times to introduce a time interval therebetween which corresponds to a pixel shift in said main scanning direction which is causes in an image reproduced from the image signals when said line sensor is displaced by said sensor displacing means, wherein said timing adjusting means comprises: a first counter for counting reference clock pulses and outputting a first timing signal for said reading clock signal upon counting said reference clock pulses up to a predetermined count; a second counter for counting said reference clock pulses and outputting a second timing signal for said drive clock signal upon counting said reference clock pulses up to a predetermined count; and offset setting means for presetting said second counter to an offset value corresponding to said time interval.

9. An image reading apparatus comprising: a line sensor having a plurality of interconnected photoelectric transducer pixels for photoelectrically reading a subject in a main scanning direction; a feed mechanism for feeding said subject with respect to said line sensor in an auxiliary scanning direction transverse to said main scanning direction for thereby two-dimensionally reading image information carried by said subject; a piezoelectric device for displacing said line sensor back and forth in said main scanning direction to shift said photoelectric transducer pixels for increasing a resolution of an image reproduced from said image information; staircase signal generating means for generating a staircase signal and supplying the staircase signal to said piezoelectric device; and a low-pass filter connected between said staircase signal generating means and said piezoelectric device.